Cathode ray amplifier



Oct. 1, 1957 D. w. DAVIS cATHoDE RAY AMPLIFIER 2 Sheets-Sheet 2 Filed Jan. 27, 1955 INVENTOR. DEAN W DAV/S gygy /Mf ATTORNEY nited States Patent CATHDE RAY AMPLIFIER Dean W. Davis, Fort Wayne, Ind., assigner to International Telephone and Telegraph Corporation Application January 27, 1955, Serial No. 484,489

4 Claims. (Cl. 313-71) The present invention relates to a cathode ray ampli- `tier, 4and more particularly to a cathode ray tube for amplifying an electron image.

This invention relates generally to the art of image storage tubes as disclosed and claimed in Farnsworth Patent No. 2,228,388. Other vcharacteristic disclosures are found in Farnsworth Patent No. 2,251,124 and in Farnsworth et al. applications Serial Nos. 197,612 and 362,473, tiled Nov. 25, 1950, and June 18, 1953, respectively. One of the primary problems encountered in the operation of storage tubes is distortion in the image display normally caused by the flood gun being onset from the writing-beam gun. In order to overcome this distortion, it is desirable to position the writing and llood guns on the tube axis. This has been attempted in the past in devices such as that ,depicted in the Farnsworth Patent No. 2,228,388, but without complete success. One diflicuglty resides in the-fact that normal scanning of the -writing beam causes unwanted detiecting movement of the ood beam.

This invention provides a construction wherebyKthe ood and writing-'guns are so disposed and operated'that ood beam deiiection does not occur when the writing beam is deflected.

In view of the foregoing it is an object of this invention to provide a cathode ray amplifier which constitutes an improvement over prior art devices.

It is another object of this invention to provide a cathode ray amplilier wherein the ood and writing beams are coaxially disposed such as to uniformly impinge the image-storage element.

Other objects will become apparent as the description proceeds.

To the accomplishment of the above and related objects, my invention may be embodied in the vforms illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that specic change maybe made in the specific constructions illustrated and described, solong as the scope of the appended claims is not violated.

In the drawings:

Fig. 1 is a sectional illustration of one embodiment of this invention;

Fig. 2 is a cross-sectional view of the ood gun of Fig. l; and

Fig. 3 is a sectional illustration of the image storage element.

Referring to Fig. l, the cathode rayvamplier comprises an envelope 1 having an enlarged funnel-shaped portion 2 anda smaller diameter c oaXially extending neck 3. M ount'edin the end of the neck v3 is a nbeam-forming or writing electron gun assembly 4 which generates a beam of electrons of elemental cross-sectional area for impinging the image storage element or screen generally indicated by the reference numeral 5. A flood electron gun 6 is mounted in the neck 3 between the gun assembly 4 and the storage element 5, and is so arranged as to emit a flood of electrons which cover either a substantial portion or theentire area of the 'screen 5. A luminescent screen 7 of conventional design and which uoresces under the impact of electrons is provided in the envelope portion 2 at the end opposite the two electron gun assemblies 4 and 6, respectively. Intubes adapted to provide an electrical signal output rather than an optical display, an ordinary conductive ,plate may be substituted for screen 7. The terms utiilization electrode or electron-receivinganode as used in the claims are intended to include both thefscreen 7 and such conductive plate. A conductive coating Sis provided internally of the neck 3 to extend between the two 'gun assemblies 4 and 6, and serves the conventional purpose of acceleratingthe-'electrons from theV gun 4 vtoward the` storage screen 5. A second conductive coating 9 is provided internally of the envelope portion 2 and extends forwardly from the ood gun 6 to a point just short of the collector screen 10. This collector screen or electrode 10 isperforate and is preferably composed of a relatively large meshmetallic screen positioned adjacent and substantially parallel to the storage screen 5.

With suitable potentials applied tothe electrodes thus far described, a Apositivetcharge image may be impressed on the storage screen 5 as it is simultaneously being ooded by electrons from the gun 6, the ilood gun .being Y maintained at a potential slightly positive with respect to the left-hand side of the screen 5. The electrons flowing therefrom will not be ,attracted to the screen itself,y but instead will Ypass throughthe screen openings to impinge the anode 7. As the 'flood electrons pass through the respective screenperforations, they are modulated by the elemental charges surrounding the perforations andwill, therefore, imp inge .the anode 7 with adensity-dependent upon such modulation. By this-means, the charge image on the screen vis optically reproduced on the anode 7.

The screen y.5, as seeninfFig. 3, is composed of a metallic screen 11, of, for example, 500 mesh, size, one side of this/screen j being covered bya rdielectric material 12, such as quartz; Exact `details of this construction. are given in Farnsworth application `Seril No..l97,6 l2, iiled Nov. ,25, 1950, and further suchsc'reens rare now being used in storage tubes commercially available on the open market. A magnetic'focusing coil 14 of conventional design surrounds the neck-Storfocusing the beam from the gun 4 onto lthe screen Sand a suitable pairof dellection coils (only one coilv 13 iswjshown.) also surrounding the neck 3 are mountedadjacent the focusingcoil 13 vfor controlling beam s cavnningof the screen5. In thisconnection, any

well-known raster-forming scanning techniques may be utilized.V I

'Of particular momentis the fact that the focusingand scanningcoils 14 and 1 3 arepositioned-rearwardly of the flood cathode 6 a distance su'ici'ent to prevent the liood beam from being altected, thereby.

The gun assembly 4 is conventionalV andfserve its, usual function of providingapeneil-like electron1-beam-for scanning, the storage screen 5. The ood kgun assembly 6, l 1 owever, is composed of an annularcathode 15 which coairially surrounds the tube faXis. It-is `Well to `note at this point that the undeiiected beam emitted by the electrongun 4rcoincides with this tube axis; This cathode 15 is preferably mounted inv an.. annular housing Y16jsuitably anchored in the tube neck 3, this housing beingjpro- Ydd .withan annular aperture 17 posi t ioned radially inwardly from the cathode 15. The central portion of the housing 16 is open as indicated by the reference numeral -18 to accommodate the deflecting movement of the electron beam from the gun 4. A suitable tubular screen 19 is mounted internally of the housing 16 to establish a uniform cylinder of potential for the writing beam passing through that region. 'Ihe `diameter of the opening 18 is of such size as to accommodate the full scanning movement of the writing beam. Mounted adjacent to the housing 16 and in coaxial relation thereto is a funnel-shaped anode element 20.

The cathode normally emits electrons radially inwardly through the annular aperture 17 toward the tube axis 21. These electrons may be considered as substantially tilling the space internally of the housing 16 such as to form a cloud of electrons of uniform cross-section. Suitable potentials are applied to the anode elements 8, 9, 20 and to the cathode 15 such that this cloud of electrons will be directed toward the front of the tube to flood the storage screen 5. The light lines of Fig. 2 emanating from the cathode 15 depict the path followed by the electrons in changing direction from radial to axial ow.

The ring 22 Vextending rearwardly from the perimeter of the collector screen 10 in conjunction with the anode 9 constitutes an electron lens which collimates the diverging flood beam 23 as illustrated. This collimated beam impinges the storage screen 5 at substantially right angles,

the electron lens being so positioned and controlled to image the source of the ood electrons appearing internally of the housing 16 in the plane of the storage screen 5. Stated in other words, the Asource or cloud of electrons inside the housing 16 is imaged in the plane of the storage screen 5, and since this source is of uniform cross-sectional density, the electron image produced on the screen S will be of uniform cross-sectional density. Suitable operating potentials for the various tube elements are indicated in Fig. l.

In operation, the beam of electrons emitted by the electron gun 4 is scanned over the screen S in the usual raster-forming manner by means of the deflection coils. The electrons in this beam are caused to travel at such velocity as to produce greater than unity secondary emission on the impinged elemental areas of the screen insulator 12, so that -as the beam is scanned over the area of this screen, a charge pattern of positive potential is formed. The low velocity electrons from the flood gun 6 are repelled lirst by the anode 8 since the potential thereof is negative with respect to the flood electrons and simultaneously is attracted toward the anode 7 by reason of the accelerating potentials applied to the anode 20. These ood electrons pass through the openings of the screen 5 before striking the screen 7. The number of flood electrons passing through the individual openings are modulated in accordance `with the charge pattern on the screen, the modulated electron flow thereby representing the charge pattern on the screen 5 and serving to excite the display of an equivalent image by the screen 7. The exact potential relationships of the Writing and flood guns as well as the storage screen 5 and anode 7 are well known, and are fully described in Farnsworth et al. application Serial No. 362,473, iiled l June 18, 1953.

By reason of the fact that the writing gun 4 is mounted on the tube axis 21 andis coaxial with the flood gun 6,

vthe usual distortion encountered by the use of an offset writing gun is eliminated. Furthermore, by positioning the focusing and deilecting coils 13 and 14 sufficiently far from the flood gun 6, the ood beam-23 will be substantially stationary Vand uniform in cross-sectional density. It may be desired to use a ferrous ring mounted on the neck 3 between the coils 13 and 14 and the flood gun 6 to further prevent interference of the magnetic fields with the flood beam 23.

What is claimed is:

1. An image signal tube comprising an ,electronreceiving anode, an image storage element disposed adjacent said anode, an electron gun for producing an electron beam of elemental cross-sectional area directed at said storage element, an additional source of electrons coaxially surrounding said beam between said electron gun and said storage element directed radially inwardly toward said beam, electrode means disposed in operative relationship to said source for turning the radially inwardly directed electrons toward said storage element and causing such turned electrons to flood said storage element.

2. An image signal tube comprising an electronreceiving anode, an image storage element disposed adjacent said anode, an electron gun for producing an electron beam of elemental ycross-sectional area directed at said storage element, an additional source of electrons coaxially surrounding said beam between said electron gun and said storage elementsaid source providing a ,vertical cathode coincident with the axis of said beam, said vertical cathode being composed of a cloud of electrons of uniform cross-sectional area which is symmetric about said axis, and electrode means adjacent to said source operative to direct and flood the electrons from said cloud onto said storage element, said electrode means including electron optic means which images said cloud in the vicinity of said storage element.

3. An image signal tube comprising an electronreceiving anode, an image storage element disposed adjacent said anode, an electron gun for producing an electron beam of elemental cross-sectional area directed at said storage element, said beam having an axial path from which it may be deected for scanning said storage element, a dood cathode symmetrically surrounding said axis and being disposed between said electron gun and said storage element, said llood cathode directing electrons radially inwardly about said axis to form a cloud of electrons of uniform cross-sectional area, and electrode means adjacent to said flood cathode operative to direct and flood the electrons fromv said cloud onto said storage element, said electrode means including means which images said cloud in the vicinity of said storage element.

4. An image signal tube comprising an electronreceiving anode, an image storage element disposed adjacent said anode, au electron gun for producing an electron beam of elemental cross-sectional Varea directed at said storage element, said beam having an axial path from which it may be deflected for scanning said storage element, an annular flood cathode symmetrically surrounding said axis and being disposed betweensaid electron gun and said storage element, the opening of said flood cathode being suliiciently large to accommodate deecting movement of said beam without interference, and accelerating anodes onV opposite sides of said ood gun serving to direct said beam onto said storage element, said lioodvcathode directing electrons radially inwardly to form a source of anodes about said axis, said accelerating electrons directing the electrons of said source Y toward said screen, and electron optical elements imaging said source on said storage element.

References Cited in the tile of this patent UNITED STATES PATENTS 2,122,095 Gabor June 28, 1936 v2,228,388 Farnsworth Ian. 14, 1941 2,251,124 Farnsworth July 29, 1941 2,452,044 Fox Oct. 26, 1948 2,503,949 Jensen et al Apr. l1, 1950 

